Aberration-corrected multibeam source, charged particle beam device and method of imaging or illuminating a specimen with an array of primary charged particle beamlets

ABSTRACT

A charged particle beam device for inspection of a specimen with an array of primary charged particle beamlets is described. The charged particle beam device includes a charged particle beam source to generate a primary charged particle beam; a multi-aperture plate having at least two openings to generate an array of charged particle beamlets having at least a first beamlet having a first resolution on the specimen and a second beamlet having a second resolution on the specimen; an aberration correction element to correct at least one of spherical aberrations and chromatic aberrations of rotational symmetric charged particle lenses; and an objective lens assembly for focusing each primary charged particle beamlet of the array of primary charged particle beamlets onto a separate location on the specimen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/642,147, filed Jul. 5, 2017, the entire contents of which areincorporated herein by reference in their entirety for all purposes.

TECHNICAL FIELD

Embodiments relate to charged particle beam devices, for example, forinspection system applications, testing system applications, defectreview or critical dimensioning applications or the like. Embodimentsalso relate to methods of operation of a charged particle beam device.More particularly, embodiments relate to charged particle beam devicesbeing multi-beam systems for general purposes (such as imagingbiological structures) and/or for high throughput EBI (electron beaminspection). Specifically, embodiments relate to a scanning chargedparticle beam device and a method of electron beam inspection with ascanning charged particle beam device.

BACKGROUND

Modern semiconductor technology is highly dependent on an accuratecontrol of the various processes used during the production ofintegrated circuits. Accordingly, the wafers are inspected repeatedly inorder to localize problems as early as possible. Furthermore, a mask orreticle is also inspected before the actual use during wafer processingin order to make sure that the mask accurately defines the respectivepattern. The inspection of wafers or masks for defects includes theexamination of the whole wafer or mask area. Especially, the inspectionof wafers during the fabrication includes the examination of the wholewafer area in such a short time that production throughput is notlimited by the inspection process.

Scanning electron microscopes (SEM) have been used to inspect wafers.The surface of the wafer is scanned using, e.g., a single finely focusedelectron beam. When the electron beam hits the wafer, secondaryelectrons and/or backscattered electrons, i.e. signal electrons, aregenerated and measured. A pattern defect at a location on the wafer isdetected by comparing an intensity signal of the secondary electrons to,for example, a reference signal corresponding to the same location onthe pattern. However, because of the increasing demands for higherresolutions, scanning the entire surface of the wafer takes a long time.Accordingly, using a conventional (single-beam) scanning electronmicroscope (SEM) for wafer inspection is difficult, since the approachdoes not provide the respective throughput.

Wafer and mask defect inspection in semiconductor technology needs highresolution and fast inspection tools, which cover both full wafer/maskapplication or hot spot inspection. Electron beam inspection gainsincreasing importance because of the limited resolution of light opticaltools, which are not able to handle the shrinking defect sizes. Inparticular, from the 20 nm node and beyond, the high-resolutionpotential of electron beam based imaging tools is in demand fordetecting all defects of interest.

Current multi-particle-beam systems may include an aperture lens array.The focal length of an aperture lens is inversely proportional to thedifference of the electric field component (along the average axis)before and after the aperture. By shaping the field distribution alongan aperture lens array, the focal length of the individual apertures canbe varied in such a way that the field curvature of the beamlets can becontrolled (or corrected). In such a configuration, other off-axialaberrations (field astigmatism, off-axial coma, and distortion) remain.To mitigate these remaining aberrations, the intermediate beamlet fociare often strongly magnified images of the source. The images of thesource are strongly demagnified with the downstream objective lens. Thistradeoff between the demagnification and remaining off-axial aberrationslimits the performance of such devices. Another way, which is oftenemployed, is to limit the total emission angle from the source (i.e.,the number of total beamlets), so that the off-axial aberrations can bereduced.

In view of the above, a charged particle beam device and a method ofimaging a specimen with an array of primary charged particle beamlets isprovided that overcome at least some of the problems in the art.

SUMMARY

In light of the above, a charged particle beam device for inspection ofa specimen with an array of primary charged particle beamlets and amethod of imaging or illuminating a specimen with an array of primarycharged particle beamlets are provided.

According to one embodiment, a charged particle beam device forinspection of a specimen with an array of primary charged particlebeamlets is provided. The charged particle beam device includes acharged particle beam source to generate a primary charged particlebeam; a multi-aperture plate having at least two openings to generate anarray of charged particle beamlets having at least a first beamlethaving a first resolution on the specimen and a second beamlet having asecond resolution on the specimen; an aberration correction element tocorrect at least one of spherical aberrations and chromatic aberrationsof rotational symmetric charged particle lenses; and an objective lensassembly for focusing each primary charged particle beamlet of the arrayof primary charged particle beamlets onto a separate location on thespecimen.

According to one embodiment, a charged particle beam device forinspection of a specimen with an array of primary charged particlebeamlets is provided. The charged particle beam device includes acharged particle beam source to generate a primary charged particlebeam; a multi-aperture plate having at least two openings to generate anarray of charged particle beamlets having at least a first beamlethaving a first resolution on the specimen and a second beamlet having asecond resolution on the specimen; an aberration correction elementprovided between the charged particle beam source and the multi-apertureplate to correct a difference of the first resolution on the specimen ascompared to the second resolution on the specimen, comprising at leasttwo multipole elements with 6 or more poles; and an objective lensassembly for focusing each primary charged particle beamlet of the arrayof primary charged particle beamlets onto a separate location on thespecimen.

According to another embodiments, a method of imaging or illuminating aspecimen with an array of primary charged particle beamlets is provided.The method includes generating an array of charged particle beamletshaving at least a first beamlet and a second beamlet by illuminating amulti-aperture plate with a primary charged particle beam; focusing thearray of charged particle beamlets on the specimen with an objectivelens assembly; and correcting aberration differences between the firstbeamlet and the second beamlet with an aberration correction element.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features can be understoodin detail, a more particular description, briefly summarized above, maybe had by reference to embodiments. The accompanying drawings relate toembodiments and are described in the following:

FIG. 1 shows a schematic view of a multi-beam device for specimeninspection;

FIG. 2 shows a schematic view of a multi-beam device for specimeninspection according to embodiments described herein and having anobjective lens array;

FIG. 3 shows a schematic view of a multi-beam device for specimeninspection according to embodiments described herein and having a lensarray and a common objective lens;

FIG. 4 shows a schematic view of a multi-beam device for specimeninspection according to embodiments described herein and having a lensarray, a deflector array, and a common objective lens;

FIG. 5A shows portions of a schematic ray path of a beam in anaberration correction element according to embodiments described herein;

FIG. 5B shows a schematic view of a beam in an aberration correctionelement according to embodiments described herein;

FIG. 6 shows a schematic view of a column array of multi-beam devicecolumns according to embodiments described herein; and

FIG. 7 shows a flow chart of a method for inspecting a specimen with acharged particle beam device according to embodiments described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to the various embodiments, one ormore examples of which are illustrated in the figures. Within thefollowing description of the drawings, the same reference numbers referto same components. The differences with respect to individualembodiments are described. Each example is provided by way ofexplanation and is not meant as a limitation. Further, featuresillustrated or described as part of one embodiment can be used on or inconjunction with other embodiments to yield yet a further embodiment.The description is intended to include the modifications and variations.

Without limiting the scope of protection of the present application, inthe following the charged particle beam device or components thereofwill exemplarily be referred to as a charged particle beam deviceincluding the detection of secondary or backscattered particles, such aselectrons. Embodiments can still be applied for apparatuses andcomponents detecting corpuscles, such as secondary and/or backscatteredcharged particles in the form of electrons or ions, photons, X-rays orother signals in order to obtain a specimen image. When referring tocorpuscles, the corpuscles are to be understood as light signals inwhich the corpuscles are photons as well as particles, in which thecorpuscles are ions, atoms, electrons or other particles. As describedherein, discussions and descriptions relating to the primary chargedparticle beam and primary charged particle beamlets are exemplarilydescribed with respect to electrons in scanning electron microscopes.Other types of charged particles, e.g. positive ions, could be utilizedas a primary charged particle beam or primary charged particle beamlets.

According to embodiments herein, which can be combined with otherembodiments, a signal (charged particle) beam, or a signal (chargedparticle) beamlet is referred to as a beam of secondary particles, i.e.secondary and/or backscattered particles. Typically, the signal beam orsecondary beam is generated by the impingement of the primary beam orprimary beamlet on a specimen or by backscattering of the primary beamfrom the specimen. A primary charged particle beam or a primary chargedparticle beamlet is generated by a particle beam source and is guidedand deflected on a specimen to be inspected or imaged.

A “specimen” or “sample” as referred to herein, includes, but is notlimited to, semiconductor wafers, semiconductor workpieces,photolithographic masks and other workpieces such as memory disks andthe like. Embodiments may be applied to any workpiece on which materialis deposited or which is structured. A specimen includes a surface to bestructured or on which layers are deposited, an edge, and typically abevel. According to some embodiments, which can be combined with otherembodiments described herein, the apparatus and methods are configuredfor or are applied for electron beam inspection, for criticaldimensioning applications and defect review applications.

A charged particle beam device 100 is shown schematically in FIG. 1. Thecharged particle beam device 100 includes a charged particle beam source110 including a particle beam emitter 111, which emits a primary chargedparticle beam 14. According to embodiments described herein, the chargedparticle beam source 110 is adapted for generating an array of primarycharged particle beamlets 15. The charged particle beam source 110 mayinclude the charged particle beam emitter 111, and a multi-apertureplate 113 having at least two openings. The primary charged particlebeam 14 may be accelerated by an accelerating voltage supplied to theacceleration electrode 199. The charged particle beam device may includeelectrodes 112-1 and 112-2.

The electrodes 112 of the charged particle beam device can be adaptedand driven to generate an electrical field on the surface of themulti-aperture lens plate. The surface of the multi-aperture plate 113may be a surface of the multi-aperture plate facing the electrode 112-2.

The charged particle beam source 110 including the beam emitter, themulti-aperture plate and the electrodes 112 may be denoted as an upperpart of the charged particle beam device. The charged particle beamdevice 100 exemplarily further includes a lens 120, an objective lens130, and a specimen stage 141, on which a specimen 140 may be placed.The lens 120, the objective lens 130, and the specimen stage 141 may bedescribed as being part of the lower part of the charged particle beamdevice. A demagnification of the emitter tip of the charged particledevice is given by the source position and the focal length of theobjective lens array.

An electric field having a z-component is generated by a voltagedifference between the electrode 112-2 and the multi-aperture plate 113.The electrical field may have a z-component extending in the z-directionof the charged particle beam device, i.e. along the optical axis 4. Thecomponent of the electrical field in the z-direction provided by theelectrodes 112 may vary over the plane of the surface of themulti-aperture lens plate.

A, for example, rotational symmetric, z-component of the electricalfield on the surface of the multi-aperture plate can be utilized for afield curvature (or image field curvature) correction by the electrodes.Further, for instance, a non-rotationally symmetric configuration of thez-component of the electrical field may be realized by a segmentedarrangement of at least one of the electrodes 112, in order to correctfor image field tilt.

The varying field of the first electrode on the surface of themulti-aperture plate in the charged particle beam device can be used forcorrecting the field curvature of the charged particle beam device, inparticular the field curvature introduced by the imaging lenses of thecharged particle beam device. More than one electrode may be used forcompensating or correcting the field curvature.

Segmented electrodes may be used to create a non-rotationally symmetricfield configuration on the surface of the multi-aperture, which can beused to correct image field tilt that may originate fromnon-rotationally symmetric optical elements or from a tilted specimen.

The charged particle beam device may include electrodes 112-1 and 112-2(two electrodes are exemplarily shown). According to some embodiments,the first electrode may be used to provide the electrical field tocreate the aperture lenses and the second electrode may be used as thefield curvature correction electrode. Further, the charged particle beamdevice 100 may include a scanning deflector 150. The scanning deflector150 can be provided between the lens 120 and the specimen stage 141.Particularly, the scanning deflector can be surrounded by a pole pieceassembly of the objective lens 130 and/or at a position of an electrodeof an electrostatic lens.

The field on the multi-aperture plate can be varied in such a way thatthe image field curvature or image field tilt of the beamlets can becontrolled (or corrected). Yet, other off-axial aberrations (e.g. fieldastigmatism, off-axial coma, and distortion) remain.

According to embodiments described herein, inspection of the specimenwith an array of primary charged particle beamlets is provided. Amulti-aperture plate is provided to generate the array of primarycharged particle beamlets from a primary charged particle beam. Themulti-aperture plate may have two or more openings. The multi-apertureplate can divide a large bundle of the primary charged particle beaminto individual beamlets, i.e. the array of primary charged particlebeamlets. An aberration correction element is provided, particularly tocorrect differences in aberrations between different beamlets of thearray of primary charged particle beamlets. According to someembodiments, which can be combined with other embodiments describedherein, the aberration correction element can correct either Cs, i.e.spherical aberrations, or both Cc and Cs, i.e. chromatic aberrations andspherical aberrations.

FIG. 2 shows a charged particle beam device 200, e.g. for inspection ofthe specimen with an array of primary charged particle beamlets. Thecharged particle beam source 110 includes a particle beam emitter 111,which emits a primary charged particle beam 14.

A collimator device such as a condenser lens assembly 220 can beprovided in the charged particle beam device, for example amulti-particle-beam system. The charged particle beam device may be usedfor particle beam inspection or particle beam lithography applications.According to some embodiments, which can be combined with otherembodiments described herein, the condenser lens assembly can includeone or more round lenses, for example, an electrostatic lens, amagnetostatic lens, or a combined magnetic electrostatic lens acting onthe primary charged particle beam emitted by the charged particle beamsource 110. Collimation devices such as the condenser lens assembly 220may include one or more electrostatic or magnetostatic lenses, which areused to create a parallel (or nearly parallel) particle beam with a beamdivergence of less than a few mrad.

Due to the spherical and chromatic aberrations, Cs and Cc of such acollimation device, large angle trajectories and trajectories ofparticles with slightly different than nominal energy are not parallelto the axis of the system, even if the paraxial trajectories withnominal energy are. This is caused by the second, third, and higherorder path deviations which cannot be avoided for conventional roundlens systems according to the Scherzer theorem.

The second and third order path deviations, i.e. second and third orderaberrations, of a round lens system have chromatic and sphericalaberrations increasing inter alia with the half angle Ω of the centraltrajectory of an individual beamlet as well as the angle ω of off-axialtrajectories within one beamlet. These aberrations may increase linearlyor quadratically with the half angle Ω and the angle ω. Further,chromatic aberrations may increase with the chromaticity parameter krelated to the energy width of the source. Resulting aberrationscorrespond to radial chromatic distortion and chromatic aberration,radial geometric distortion, radial field astigmatism, field curvature,radial off-axial coma, and spherical aberration. All of those abovementioned aberrations (except for the chromatic and sphericalaberration) depend on the beamlet angle Ω and hence lead to anon-uniformity from beamlet to beamlet and therefore cause a non-uniformresolution on the specimen.

According to embodiments described herein, an aberration correctionelement 210 is provided. The aberration correction element is used tocorrect the spherical and/or chromatic aberration coefficients, Cs andCc, of the collimator lens, and optionally in addition of the objectivelens. The above referenced second and third order aberrations of theprimary charged particle beam may be considered as the cause of thefield curvature aberration between the primary charged particlebeamlets. Thus, the field curvature of a beamlet array may be correctedby controlling the corresponding chromatic and spherical aberrations ofthe primary charged particle beam, i.e. the assembly of the beamlets.For example, the aberration correction element may generateelectro-magnetic quadrupole fields. FIG. 2 shows a first magneticquadrupole 212, the first electromagnetic quadrupole 214, a secondelectromagnetic quadrupole 216, and a second magnetic quadrupole 218.The resulting corrections are shown by beam paths 14′ in a Y-Z-plane andbeam paths 14″ in an X-Z-plane. As can be seen, beam trajectories withdifferent energies (see different lines) exit the aberration correctionelement 210 parallel or essentially parallel to the optical axis,thereby correcting the chromatic aberration. Additionally, superposedoctupole fields may be used to correct for spherical aberrations.Corresponding octupoles are for example shown in FIG. 2. A firstoctupole 215 can be superposed with the first electromagnetic quadrupole214. A third octupole 219 can be superposed with the firstelectromagnetic quadrupole 216. A second octupole 217 can be providedbetween the first octupole and the third octupole, e.g. in the middle ofthe two octupoles. According to some embodiments, which can be combinedwith other embodiments described herein, it is beneficial if theaberration correction element 210 is symmetric, i.e. the quadrupoles andthe octupoles are symmetric to a symmetry plane orthogonal to theoptical axis.

According to yet, further embodiments, the above described aberrationcorrection element 210 can be modified by having four or more octupoles.For example, four octupoles can be superposed with respective ones ofthe quadrupoles denoted with reference numerals 212, 214, 216, and 218.

According to yet further embodiments, further modifications of anaberration correction element 210 can include the quadrupoles 212 and218 may also be electrostatic or combined magnetic electrostatic.

According to some embodiments, which can be combined with otherembodiments described herein, an aberration correction element 210 cancorrect or compensate Cc, Cs, or both Cc and Cs.

According to yet further embodiments, in the case that the energy widthof the source is sufficiently small enough, a simpler Cs corrector(e.g., hexapole fields and transfer doublet) may be used, as long as thechromatic effects can be neglected. Accordingly, an aberrationcorrection element 210 may alternatively include a first electric ormagnetic hexapole and a second electric or magnetic hexapole. A transferlens system consisting of at least one lens can be provided to provide asymmetric ray path through the field arrangements. The symmetricalarrangement allows for correcting the spherical aberration whilepreventing the introduction of second order geometric aberrations, e.g.the threefold astigmatism. By utilizing an aberration correction elementaccording to embodiments described herein, the parallelism of theindividual beamlets may be limited only due to path deviations of afourth or higher order as well as imperfections of the aberrationcorrection element.

According to embodiments described herein, the aberration correctionelement can be a non-rotationally symmetric multipole corrector. Forexample, a quadrupole-octupole corrector for simultaneous correction ofCs and Cc or a double hexapole corrector for Cs correction can beprovided. Embodiments include at least two multipole elements with 6 ormore poles, e.g. hexapole elements, octupole elements, or even higherorder multipole elements. According to yet further embodiments, whichcan be combined with other embodiments described herein, the aberrationcorrection element is configured to operate at fixed excitation at alltimes and/or for various operation modes.

According to yet further embodiments, which can be combined with otherembodiments described herein, the aberration correction element can beconfigured to correct at least one of spherical aberrations andchromatic aberrations of rotationally symmetric charged particle lenses.For example, the aberration correction element is configured to correctthe difference between the first resolution on the specimen and thesecond resolution on the specimen and comprises at least two multipoleelements with each consisting of 6 or more poles. According to yetfurther examples or modifications, which can be combined with otherembodiments described herein, the aberration correction element can beselected from the group consisting of: a foil lens, a membranecorrector, wherein the primary electrons trespass a membrane of varyingthickness, a space charge lens, a high frequency lens, and a mirrorcorrector.

Due to the increasing demand for high throughput particle beaminspection devices, charged particle beam devices with an array ofprimary charged particle beamlets, i.e. multi-beam systems, have beensuggested. At least two beams are scanned across the specimen within thesame column or device. A charged particle beam device may include ascanning deflector 150 as described with respect to FIG. 1. The array ofprimary charged particle beamlets is provided by creating acomparatively large collimated particle beam which is then divided intomultiple parallel beamlets by a multi-aperture array 113 as, e.g., shownin FIG. 2. The primary charged particle beamlets 15 are focused on thespecimen 140 by an objective lens assembly 230. As shown in FIG. 2, theobjective lens assembly can be an objective lens array. The objectivelens array can include multiple individual lenses used to focus thebeamlets onto the specimen, e.g. onto a separate location on thespecimen. The specimen can be supported on a specimen stage 141.

The radial geometric and chromatic distortion (outer beamlets are notparallel to the central beamlets), radial field astigmatism (outerbeamlets are astigmatic), field curvature (outer beamlets are more orless converging or diverging within themselves compared with innerbeamlets), and radial off-axial coma (outer beamlets exhibit comaaberration) may result in a varying resolution on the specimen dependingon the off-axial distance of the beamlet. Accordingly, embodimentsdescribed herein provide an aberration correction element 210 to correctfor a varying resolution of the beamlets. The beamlets may havevanishing Cc and Cs before entering the objective lens assembly. Usingsuch a device is capable of producing beamlets which are (up to thethird order) parallel with respect to each other and within themselves.A multi-beam system according to embodiments described herein may, thus,improve the resolution uniformity on the specimen.

FIG. 3 shows another embodiment of a charged particle beam device 200having an array of primary charged particle beamlets. A primary chargedparticle beam is generated by the charged particle beam source 110. Anaberration correction element 210 is provided, wherein aspects, details,and optional modifications can be used as described with respect to FIG.2. A comparably wide primary charged particle beam, which can forexample be parallel, illuminates the multi-aperture plate 113. An arrayof primary charged particle beamlets 15 is generated. A lens array 320creates individual crossovers 315. For example, the lens array creatingthe intermediate crossovers may, e.g., include Einzel lenses or aperturelenses. A common objective lens 130 focuses the beamlets on different orseparate locations on the specimen 140.

In FIG. 3, the objective lens 130 is schematically illustrated. Anobjective lens 130 can be provided for embodiments described herein asshown in more detail in FIG. 1. The objective lens may include a coiland upper and lower pole pieces, wherein a magnetic lens component forthe array of primary charged particle beamlets is provided. Further, anupper electrode and a lower electrode may provide an electrostatic lenscomponent of the objective lens 130. A demagnification of the emittertip of the charged particle device is given by the source position andthe focal length of the objective lens array.

According to some optional modifications yielding yet furtherembodiments, a possibly existing fifth order spherical aberrationcoefficient C5 can be adjusted by an appropriate distance between thecondenser lens array and the aberration correction element.

Particularly, the objective lens can be a combined magneticelectrostatic lens. The electrostatic lens component can, according tosome embodiments, provide a deceleration lens, wherein the landingenergy of the beamlets on the specimen can be reduced as compared to theenergy of the beamlets within the column. For example, the landingenergy can be between about 100 eV and 8 keV, more typically 2 keV orless, e.g. 1 keV or less, such as 500 eV or even 100 eV. The beam energyof the beamlets within the column can be 5 keV or above, such as 20 keVor above, or even 50 keV or above.

In some embodiments, which may be combined with other embodimentsdescribed herein, the objective lens 130 may be a field compound lens.For instance, the objective lens may be a combination of a magnetic lenscomponent and an electrostatic lens component. Accordingly, theobjective lens may be a compound magnetic-electrostatic lens. Typically,the electrostatic part of the compound magnetic-electrostatic lens is anelectrostatic retarding field lens. Using a compoundmagnetic-electrostatic lens yields superior resolution at low landingenergies, such as a few hundred electron volts in the case of a scanningelectron microscope (SEM). Low landing energies are beneficial,especially in the modern semiconductor industry, to avoid the chargingand/or the damage of radiation sensitive specimens.

Further, the charged particle beam device 200 may include a scanningdeflector 150. The scanning deflector 150 can be provided between thelens and the specimen stage 141. Particularly, the scanning deflectorcan be surrounded by a pole piece assembly of the objective lens 130and/or at a position of an electrode of the electrostatic lenscomponent.

According to some embodiments, which can be combined with otherembodiments described herein, it is also possible to operate thecorrection element, i.e. the Cc-Cs corrector having two or moremultipole elements, as a lens. The aberration correction element canfocus the primary charged particle beam to reduce a divergence between afirst beamlet and a second beamlet, for example to generate parallelbeamlets. Accordingly, a condenser lens or a condenser lens assemblycollimating the primary charged particle beam before impingement on themulti-aperture plate can be optional for some configurations.

Further, for embodiments utilizing a common objective lens (see e.g.FIGS. 3 and 4), the aberration correction element, i.e. the Cc-Cscorrector can be operated to not fully correct the aberrations of thelens array and an optionally existing condenser lens assembly. Theaberration correction element 210 in combination with the lens array 320can provide an array of intermediate beamlet crossovers which possessthe opposite off-axial aberrations (field curvature, field astigmatism,radial chromatic distortion, etc.) as the common objective lens. Forembodiments having a common objective lens and a condenser lensassembly, the aberration correction element may be operated to not fullycorrect the aberrations of the condenser lens. The operation may be tocreate an array of intermediate beamlet crossovers which possess theopposite off-axial aberrations (field curvature, field astigmatism,radial chromatic distortion, etc.) as the common objective lens. Thus,according to some embodiments, the Cc-Cs corrector within the collimatorcan be used to create defined field curvature, field astigmatism, andradial chromatic distortion, which cancel the inherent off-axialaberrations of the common objective lens.

In FIG. 3 the beamlets pass the objective lens without going through acommon crossover. The Cc-Cs corrector within the collimator can beadjusted in such a way that the off-axial coma of the objective lens iscorrected. Because of the avoiding of a common crossover, Coulomb orelectron-electron interactions, that can lead to a deterioration of theresolution on the specimen, can be reduced.

Further, the charged particle beam device 200 may include a scanningdeflector 150. The scanning deflector 150 can be provided within theobjective lens or between the lens and the specimen stage 141.Particularly, the scanning deflector can be surrounded by a pole pieceassembly of the objective lens and/or at a position of an electrode ofthe electrostatic lens component.

FIG. 4 shows another embodiment of a charged particle beam device 200.An additional deflection element 450 having deflectors 454 and,optionally also a further lens 452 close to the intermediate crossoverplane may be used to adjust an off-axial coma of the beamlets. Thebeamlets may be deflected on a “coma-free” path. Alternatively, thedeflection element 450 guiding the beamlets through a coma-free point ofthe objective lens can include the further lens 452, whereas thedeflector array having the deflectors 454 can be optional. Accordingly,the deflection element 450 can include the further lens 452, thedeflector arrays having the deflectors 454, or both.

According to some embodiments, a deflector array may be arranged withinor near the further lens. According to some embodiments, the deflectorarray being arranged “in or near” or “within” the further lens may beunderstood in that the deflector array is placed within the focal lengthof the further lens. For instance, the further lens may include threeelectrodes and the deflector array may be placed within the threeelectrodes. According to some embodiments, the deflector array mayapproximately be placed at the height of the middle electrode of thethree electrodes of the further lens.

According to some embodiments, the further lens may be used forachieving the main effect of directing the primary charged particlebeamlets, for instance for directing the primary charged particlebeamlets to the coma free point of the objective lens. A deflector arraymay be used in some embodiments for fine adjustment of the individualprimary charged particle beamlets, especially the fine adjustment of theprimary charged particle beamlets to be guided into or through the comafree point of the objective lens.

As used throughout the present disclosure, the term “coma-free plane” or“coma-free point” refers to a plane or a point of (or provided by) theobjective lens at which minimum or even no coma is introduced in theprimary charged particle beamlets when the primary charged particlebeamlets pass through the coma-free point or coma-free plane. Thecoma-free point or coma-free plane of the objective lens is a point orplane of the objective lens at which the Fraunhofer condition (thecondition that the coma is zero) is satisfied. The coma-free point orcoma-free plane of the objective lens is located on a z-axis of theoptical system of the charged particle beam device, wherein the z-axisextends along the optical axis 4 (see FIG. 1) of the objective lens. Thecoma-free point or coma-free plane can be positioned within theobjective lens. For example, the coma-free point or coma-free plane canbe surrounded by the objective lens.

According to embodiments described herein, the charged particle beamdevice and the method for inspecting a specimen with an array of primarycharged particle beamlets described herein allow for correcting off-axisaberrations for compensating differences in resolution between differentbeamlets of the array of primary charged particle beamlets. Embodimentsdescribed herein thus allow for a system, wherein off-axial aberrationswould only or mainly result from 4th or higher order aberrations of,e.g., the condenser-corrector system.

Embodiments of charged particle beam devices 200, as exemplarily shownin FIGS. 2, 3, 4, and 6, may include the further optional modificationto yield yet further embodiments. A charged particle beam emitter 111 ofthe charged particle beam source 110 may be a cold field emitter (CFE),a Schottky emitter, a TFE or another high current high brightnesscharged particle beam source (such as an electron beam source). A highcurrent is considered to be 5 μA in 100 mrad or above, for example up to5 mA, e.g. 30 μA in 100 mrad to 1 mA in 100 mrad, such as about 300 μAin 100 mrad. According to some implementations, the current isdistributed essentially uniform, e.g. with a deviation of +−10%,particularly in the case of a linear or rectangular array.

According to yet further embodiments, which can be combined with otherembodiments described herein, a TFE or another high reduced-brightnesssource, e.g. an electron-beam source, capable of providing a large beamcurrent is a source where the brightness does not fall by more than 20%of the maximum value when the emission angle is increased to provide amaximum of 10 μA-100 μA, for example 30 μA. According to someembodiments, which may be combined with other embodiments describedherein, the objective lens array may include individual electrostaticlenses (in particular retarding field lenses). In some embodiments, anobjective lens array may be used in embodiments described hereinincluding individual magnetic lens pieces, in particular having a commonexcitation coil. According to some embodiments, an objective lens arrayused for a charged particle beam device according to embodimentsdescribed herein may include a combination of individual electrostaticlenses and individual magnetic lenses. Alternatively, a common objectivelens can be used as described with respect to FIGS. 3 and 4.

In the embodiments described with regard to FIGS. 2, 3, 4 and 6, theprimary charged particle beam 14 can pass through the multi-apertureplate 113 after having left the charged particle beam emitter 111, i.e.the emitter tip. The primary charged particle beam 14 passes through themulti-aperture plate 113 having multiple aperture openings. The apertureopenings can be situated in any array configuration on themulti-aperture plate 113 such as a line, rectangle, a square, a ring, orany suitable one-dimensional or two-dimensional array. According toembodiments described herein, the charged particle beam device asdescribed herein allows for arraying the aperture openings of themulti-aperture plate in any configuration without having drawbacks dueto field curvature or aberrations. For instance, known systems arrangethe different beamlets in a ring-like shape for providing the sameconditions for every beam passing a lens acting like a parabola. Whenarranging the beamlets on a ring-like shape, the aberration influence ofthe respective lens may be minimized. Yet, a ring-shaped arrangementprovides limitations for high throughput. With the charged particle beamdevice according to embodiments described herein, the arrangement of thebeamlet array may be done in any arrangement, e.g. an arrangementsuitable for fast inspection, an arrangement adapted to the specimenstructure to be inspected, an arrangement allowing a large number ofbeams, an arrangement adapted to the beam intensity and the like. Forexample, the beamlet array may be arranged in a line, a rectangle, ahexagon, or a square.

In some embodiments, the array of primary charged particle beamlets maybe arranged in a one dimensional (line) arrays or 2-dimensional arrays(e.g. 4×4, 3×3, 5×5) or asymmetrical arrays e.g. 2×5. Embodimentsdescribed herein are not limited to the examples of arrays and mayinclude any suitable array configuration of primary charged particlebeamlets.

By illuminating the multi-aperture plate 113 with the primary chargedparticle beam 14, several primary charged particle beamlets 15 arecreated. In the focus plane of the primary charged particle beamlets 15,a lens 120 may be arranged.

In the figures, some of the primary charged particle beamlets of thearray of primary charged particle beamlets are shown after the lens,while other primary charged particle beamlets are omitted in thedrawings for the sake of a better overview.

According to some embodiments, which can be combined with otherembodiments described herein, the aberration correction element may bean electrostatic corrector, i.e. electrostatic multipoles are includedin the aberration correction element. The electrostatic corrector canbe, for example, purely electrostatic, i.e. not including magneticmultipoles. This may be beneficial for arraying multiple columns asdescribed with respect to FIG. 6 below. For example, the aberrationcorrection element can include electrostatic lens fields andelectrostatic quadrupole fields for chromatic aberration correction.Additionally, electrostatic octupole fields may be superposed forspherical aberration correction. The electrostatic lens fields can besuperposed with the quadrupole fields. The resulting corrections areshown by beam paths 14′ in a Y-Z-plane and beam paths 14″ in anX-Z-plane in FIG. 5A. An electrostatic corrector may be beneficial forallowing reduced space when having an array of two or more columns,wherein each column may provide a multi-beam charged particle device.Further benefits may be that hysteresis is avoided and the fieldprecision is mainly limited by machining tolerances. This is for exampledescribed in “Electrostatic correction of the chromatic and of thespherical aberration of charged-particle lenses” by ChristophWeißbäcker, Harald Rose in J Electron Microsc (Tokyo) (2001) 50 (5):383-390.

A combined magnetic electrostatic aberration correction element canbenefit from decoupling focusing properties and Cc correction, moderatehigher order aberrations, moderate sensitivity to alignment errors, anddamping of noise in the magnetic circuits to the low kHz range.

An exemplary embodiment of an electrostatic aberration correctionelement 210 is shown in FIG. 5B. The corrector includes a plurality ofelectrostatic multipoles and lenses, which are, for example,beneficially symmetrically arranged. That is there is a symmetry planeof the aberration correction element, which is orthogonal to the opticalaxis. For example, elements 512 can be electrostatic quadrupoles,elements 514 can be a combination of electrostatic lenses superposedwith electrostatic quadrupoles. Elements 512 and 514 can correct Cc. Theelements 513 and 515 can be electrostatic octupoles for correction ofCs. An aberration correction element 210 can include elements to correctCc, Cs, or both Cc and Cs.

As mentioned above, the charged particle beam device according toembodiments described herein allows for providing an array of primarycharged particle beamlets. According to some embodiments, the array ofprimary charged particle beamlets may typically include three or moreprimary charged particle beamlets per column, more typically ten or moreprimary charged particle beamlets. According to some embodimentsdescribed herein, the charged particle beam device and the method forinspecting a sample with a charged particle beam device according toembodiments described herein may provide an array of primary chargedparticle beamlets within one column of a charged particle beam devicehaving a small distance to each other at the sample surface. Forinstance, the distance between two primary charged particle beamletswithin one column may typically be less than 150 μm, more typically lessthan 100 μm, or even less than 50 μm.

In some embodiments, as exemplarily shown in FIG. 6, the chargedparticle beam device according to embodiments described herein allows tobe arrayed in a multi-column microscope (MCM). Multiple columns eachhaving an array of primary charged particle beamlets for inspecting aspecimen increases the process speed and throughput.

FIG. 6 shows a multi-column microscope configuration 600. Themulti-column microscope configuration 600 is exemplarily shown withthree charged particle beam devices 200. The number of charged particlebeam devices may deviate from the shown example in multi-columnmicroscope configuration according to embodiments described herein. Forinstance, a multi-column microscope configuration according toembodiments described herein may have two or more charged particle beamdevices, such as two, three, four, five, or even more than five chargedparticle beam devices. The charged particle beam devices can be arrangedin a 1-dimensional or a 2-dimensional array. Each of the chargedparticle beam devices of the multi-column microscope configuration maybe a charged particle beam device having an array of primary chargedparticle beamlets as described in any of the embodiments describedherein.

In the exemplary view of FIG. 6, the multi-column microscope includescharged particle beam devices as shown and described in FIG. 2. Themulti-column microscope configuration 600 includes a specimen stage 141on which a specimen 140 to be inspected is placed. In some embodiments,the charged particle beam devices of the multi-column microscopeconfiguration 600 may inspect one specimen. Alternatively, more than onespecimen 140 may be placed on the specimen stage 141.

As shown in FIG. 6, each charged particle beam device 200 includes acondenser lens assembly having, for example, one or more condenserlenses, an aberration correction element 210, the multi-aperture plate113, and a lens array, e.g. objective lens assembly 230. According tosome embodiments described herein, the charged particle beam devices 200of the multi-column microscope configuration 600 may have a commonobjective lens assembly.

Additionally a control electrode, e.g. a proxi-electrode, for extractingthe signal particles, such as secondary electrons (SE) or backscatteredelectrons, may be provided for charged particle beam devices ofembodiments described herein and/or multi-column microscopeconfigurations 600. The control electrode can be a common electrode formore than one column or can be a control electrode for one column. Forinstance, with objective lenses as described for embodiments of thepresent disclosure, the very low landing energy, e.g. 100 eV and a lowextraction field, can be provided without deteriorating the overallperformance of the charged particle beam imaging system.

According to some embodiments, the charged particle beam devices 200 ofthe multi-column microscope configuration may have a distance to eachother of typically between about 10 mm to about 60 mm, more typicallybetween about 10 mm and about 50 mm. In some embodiments, the distancebetween the single charged particle beam devices of the multi-columnmicroscope configuration may be measured as the distance between thecorresponding optical axes of the charged particle beam devices.

By using several charged particle beam devices in a multi-columnmicroscope configuration as exemplarily shown in FIG. 6, a sufficientnumber of primary charged particle beamlets can be provided at asufficient resolution and with a sufficiently small crosstalk betweensignal beamlets.

FIG. 7 shows a flowchart of a method 700 of imaging a specimen with anarray of primary charged particle beamlets. In block 701 an array ofcharged particle beamlets is generated by illuminating a multi-apertureplate with the primary charged particle beam. The area of chargedparticle beamlets may have at least a first beamlet and a secondbeamlet. The primary charged particle beam can be generated with acharged particle beam source including a beam emitter. The beam emittermay for instance be a CFE, a Schottky emitter, a TFE or another highcurrent—high brightness charged particle beam source (such as anelectron beam source), as e.g. mentioned above. According to someembodiments, the beam emitter may emit one primary charged particlebeam, which may be processed (e.g. by being split up by a multi-apertureplate) so that a plurality of primary charged particle beamlets aregenerated. For instance, the aperture openings in the multi-apertureplate may be arranged into a 1-dimenional beamlet array, or a2-dimensional beamlet array, such as—for instance—a hexagonal, arectangular or quadratic beamlet array

As indicated by block 702, the array of charged particle beamlets isfocused on a specimen, for example with an objective lens assembly. Theobjective lens assembly may be an objective lens array or a commonobjective lens assembly. For example, an objective lens array mayinclude two or more electrostatic lenses and/or two or more magneticlenses. A common objective lens assembly may include a magnetic lenscomponent and an electrostatic lens component, particularly anelectrostatic lens component operating in a deceleration mode.

As indicated by block 703, aberration differences within the array ofprimary charged particle beamlets, for example differences inaberrations and/or resolution between the first beamlet and the secondbeamlet, can be corrected with an aberration correction element. Theaberration correction element can correct either Cs, i.e. sphericalaberrations, or both Cc and Cs, i.e. chromatic aberrations and sphericalaberrations. According to embodiments described herein, the aberrationcorrection element can be a non-rotationally symmetric multipolecorrector. For example, a quadrupole-octupole corrector for simultaneouscorrection of Cs and Cc or a double hexapole corrector for Cs correctioncan be provided.

According to some embodiments, the aberration correction element may acton the primary charged particle beam or may act on the primary chargedparticle beamlets. Yet further, additionally or alternatively, for acommon objective lens assembly, the aberration correction element maycorrect off-axial aberrations of the objective lens assembly. For anobjective lens array, the beamlets may enter the lenses of the objectivelens array along the optical axis. Accordingly, correction of thecondenser lens assembly (and optionally further lenses) may be providedby the aberration correction element. According to yet furtherembodiments, which can be combined with other embodiments describedherein, the aberration correction element may act as a collimator lens,wherein a condenser lens assembly may be omitted.

According to some embodiments described herein, the charged particlebeam device may include further beam optical elements, such as condenserlenses, (scanning) deflectors, beam benders, correctors, or the like. Insome embodiments, a condenser lens may be placed before themulti-aperture plate (i.e. upstream of the primary charged particle beamwhen seen in a direction of the propagating primary charged particlebeam). The charged particle beam device according to embodimentsdescribed herein may include a beam blanker, such as an individual beamblanker for each beamlet or a common beam blanker.

According to yet further embodiments, which can be combined with otherembodiments described herein, a condenser lens assembly may include oneor more condenser lenses. Each of the condenser lenses can beelectrostatic, magnetic or combined magnetic electrostatic. According tosome embodiments, the multi-aperture plate, i.e. an array of apertureopenings may be replaced with a different multi-aperture plate, forexample for changing the diameters of the aperture openings. Thisenables for switching between different beamlet currents. Particularlyfor exchanging multi-aperture plates, the condenser lens assembly caninclude two or more condenser lenses for adjusting the focal length.Adjusting the focal length can be advantageous for adjusting the totalmagnification of the source. As described above, the charged particlebeam device as described herein may be used for particle beam inspectionor particle beam lithography applications. Further, the methods ofimaging a specimen with an array of primary charged particle beamletscan similarly apply to a method of illuminating a specimen with an arrayof primary charged particle beamlets, for example for particle beamletlithography applications.

While the foregoing is directed to embodiments, other and furtherembodiments may be devised without departing from the basic scopethereof, and the scope thereof is determined by the claims that follow.

1.-21. (canceled)
 22. A charged particle beam device for inspection of aspecimen with an array of primary charged particle beamlets, comprising:a charged particle beam source to generate a primary charged particlebeam; a multi-aperture plate having at least two openings to generate anarray of primary charged particle beamlets having at least a firstbeamlet having a first resolution on the specimen and a second beamlethaving a second resolution on the specimen; an aberration correctionelement to correct at least one of spherical aberrations and chromaticaberrations of rotationally symmetric charged particle lenses, theaberration correction element being arranged such that the primarycharged particle beamlets enter the aberration correction element at afirst end and exit at an opposite end; and an objective lens assemblyfor focusing each primary charged particle beamlet of the array ofprimary charged particle beamlets onto a separate location on thespecimen.
 23. The charged particle beam device according to claim 22,wherein the aberration correction element is configured to correct thedifference between the first resolution on the specimen and the secondresolution on the specimen and comprises at least two multipoleelements.
 24. The charged particle beam device according to claim 23,wherein the at least two multipole elements each consists of 6 or morepoles.
 25. The charged particle beam device according to claim 23,wherein the at least two multipole elements generate at least twohexapole fields.
 26. The charged particle beam device according to claim25, wherein the aberration correction element further comprises at leastone electrostatic or magnetic lens.
 27. The charged particle beam deviceaccording to claim 23, wherein the at least two multipole elements aretwo combined electric-magnetic quadrupole elements and the aberrationcorrection element further comprises two electric or magnetic quadrupoleelements.
 28. The charged particle beam device according to claim 27,wherein the aberration correction element further comprises at leastthree electric or magnetic octupole elements.
 29. The charged particlebeam device according to claim 22, wherein the aberration correctionelement further comprises at least three electric octupole elements. 30.The charged particle beam device according to claim 22, wherein theaberration correction element is provided between the charged particlebeam source and the multi-aperture plate.
 31. The charged particle beamdevice according to claim 30, wherein the aberration correction elementfocuses the primary charged particle beam to reduce a divergence betweenthe first beamlet and the second beamlet.
 32. The charged particle beamdevice according to claim 22, wherein the aberration correction elementis provided between the multi-aperture plate and the objective lensassembly, and wherein the aberration correction element actssimultaneously on at least the first beamlet and the second beamlet. 33.The charged particle beam device according to claim 22, furthercomprising: a condenser lens assembly provided between the chargedparticle beam source and the multi-aperture plate.
 34. The chargedparticle beam device according to claim 22, wherein the objective lensassembly comprises an objective lens array to focus each beamlet of thearray of primary charged particle beamlets individually.
 35. The chargedparticle beam device according to claim 22, wherein the objective lensassembly comprises a magnetic lens component acting on the array ofprimary charged particle beamlets.
 36. The charged particle beam deviceaccording to claim 35, further comprising: a lens array provided betweenthe multi-aperture plate and the objective lens assembly.
 37. Thecharged particle beam device according to claim 35, further comprising:at least one of a lens or a deflector array, wherein the lens and thedeflector array guides the array of primary charged particle beamletsthrough a coma free point of the objective lens assembly.
 38. A chargedparticle beam device for inspection of a specimen with an array ofprimary charged particle beamlets, comprising: a charged particle beamsource to generate a primary charged particle beam; a multi-apertureplate having at least two openings to generate an array of primarycharged particle beamlets having at least a first beamlet having a firstresolution on the specimen and a second beamlet having a secondresolution on the specimen; an aberration correction element to correctat least one of spherical aberrations and chromatic aberrations ofrotationally symmetric charged particle lenses; and an objective lensassembly for focusing each primary charged particle beamlet of the arrayof primary charged particle beamlets onto a separate location on thespecimen; wherein the aberration correction element is along an opticalaxis extending from the charged particle beam source to an objectivelens assembly.
 39. A charged particle beam device for inspection of aspecimen with an array of primary charged particle beamlets, comprising:a charged particle beam source to generate a primary charged particlebeam; a multi-aperture plate having at least two openings to generate anarray of primary charged particle beamlets having at least a firstbeamlet having a first resolution on the specimen and a second beamlethaving a second resolution on the specimen; an aberration correctionelement to correct at least one of spherical aberrations and chromaticaberrations of rotationally symmetric charged particle lenses; and anobjective lens assembly for focusing each primary charged particlebeamlet of the array of primary charged particle beamlets onto aseparate location on the specimen; wherein the aberration correctionelement is arranged such that the primary charged particle beamlets passthrough the aberration correction element once.